Tire with Component Containing Asphaltene

ABSTRACT

The present invention is directed to a pneumatic tire including at least one component, the at least component including a rubber composition, the rubber composition including 100 parts by weight of a diene based elastomer and from 1 to 20 parts by weight, per 100 parts by weight of elastomer (phr), of a solvent-extracted asphaltene.

BACKGROUND OF THE INVENTION

There has been an increasing demand to develop tires with a high levelof handling performance, good stability and steering response whenchanging lanes, avoiding obstacles on the road and cornering. Improvedroad grip without compromising stability is critical for vehiclestraveling at high speed. However, higher tire operating temperatures areencountered at high speeds than are experienced during normal drivingand the hot rubber in the tire becomes more pliable which reduces thehandling stability of the tire, a so-called “borderline” use of saidtire.

A widely adopted method to improve stability, particularly road grippingproperties, is to increase the hysteresis loss of tread rubbercompositions. A large hysteresis loss during the deformation of tread isused for increasing a friction force between the tread and road surface.However, a significant increase of heat buildup will occur during therunning of the tires as the hysteresis loss of the tread rubber becomeslarge, causing wear resistance of the tread rubber to deterioraterapidly. On the other hand, it is believed that controllability issignificantly influenced by hardness (which is closely related tocornering stiffness of a tire) and breaking strength of rubbercompositions. In order to enhance controllability, especially steeringresponse, it is necessary to increase the stiffness of the tire compoundin general and the tread in particular, which in most cases results inlower hysteresis loss. Therefore, it is very difficult to achieve bothof these desired properties by conventional compounding techniques.

SUMMARY OF THE INVENTION

The present invention is directed to a pneumatic tire comprising atleast one component, the at least component comprising a rubbercomposition, the rubber composition comprising 100 parts by weight of adiene based elastomer and from 1 to 20 parts by weight, per 100 parts byweight of elastomer (phr), of a solvent-extracted asphaltene.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a pneumatic tire comprising at least one component,the at least component comprising a rubber composition, the rubbercomposition comprising 100 parts by weight of a diene based elastomerand from 1 to 20 parts by weight, per 100 parts by weight of elastomer(phr), of a solvent-extracted asphaltene.

Asphaltene generally includes the fraction of petroleum that isinsoluble in n-pentane. By solvent-extracted, it is meant that theasphaltene has been extracted from an asphaltene-containing resin usingsuitable solvents following procedures as are known in the art.Asphaltene-containing resins may include any petroleum-based resins ormixed resins containing asphaltenes. Petroleum-based resins include butare not limited to asphalt. Mixed resins include but are not limited tocommercially available resins such as Struktol 40MS. In one embodiment,the solvent-extracted asphaltene is a pentane-extracted asphaltene thathas been extracted from an asphaltene-containing resin using n-pentane.In one embodiment, the solvent extracted asphaltene is asphaltene thathas been extracted from an asphaltene-containing resin using propane forinitial extraction and precipitation, followed by purification withn-pentane or n-heptane.

In one embodiment, the solvent-extracted asphaltene comprises sulfurcontent of greater than 5 percent by weight, based on the total weightof the asphaltene. In one embodiment, the solvent-extracted asphaltenecomprises sulfur content of greater than 7 percent by weight, based onthe total weight of the asphaltene. In one embodiment, thesolvent-extracted asphaltene comprises sulfur content of greater than 8percent by weight, based on the total weight of the asphaltene. Highsulfur containing asphaltenes may originate in resins derived frompetroleum from the Athabasca fields of western Canada or the Boscanfields of Venezuela.

In one embodiment, the solvent-extracted asphaltene is present in therubber composition in a concentration ranging from 1 to 20 parts byweight per 100 parts by weight of diene based elastomer (phr). Inanother embodiment, the solvent-extracted asphaltene is present in therubber composition in a concentration ranging from 1 to 15 parts byweight per 100 parts by weight of diene based elastomer (phr). Inanother embodiment, the solvent-extracted asphaltene is present in therubber composition in a concentration ranging from 5 to 15 parts byweight per 100 parts by weight of diene based elastomer (phr).

The rubber composition may be used with rubbers or elastomers containingolefinic unsaturation. The phrases “rubber or elastomer containingolefinic unsaturation” or “diene based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polybutadiene and SBR.

In one aspect the rubber is preferably of at least two of diene basedrubbers. For example, a combination of two or more rubbers is preferredsuch as cis 1,4-polyisoprene rubber (natural or synthetic, althoughnatural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include from 5 to 70 phr of processingoil. Processing oil may be included in the rubber composition asextending oil typically used to extend elastomers. Processing oil mayalso be included in the rubber composition by addition of the oildirectly during rubber compounding. The processing oil used may includeboth extending oil present in the elastomers, and process oil addedduring compounding. Suitable process oils include various oils as areknown in the art, including aromatic, paraffinic, naphthenic, vegetableoils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenicoils. Suitable low PCA oils include those having a polycyclic aromaticcontent of less than 3 percent by weight as determined by the IP346method. Procedures for the IP346 method may be found in Standard Methodsfor Analysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The phrase “rubber or elastomer containing olefinic unsaturation” isintended to include both natural rubber and its various raw and reclaimforms as well as various synthetic rubbers. In the description of thisinvention, the terms “rubber” and “elastomer” may be usedinterchangeably, unless otherwise prescribed. The terms “rubbercomposition,” “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials, and such terms are well known tothose having skill in the rubber mixing or rubber compounding art.

The rubber composition may include from about 10 to about 150 phr ofsilica.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil™ with designations 210, 243, etc;silicas available from Rhodia, with, for example, designations ofZ1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

The vulcanizable rubber composition may include from 1 to 100 phr ofcarbon black, crosslinked particulate polymer gel, ultra high molecularweight polyethylene (UHMWPE) or plasticized starch.

Commonly employed carbon blacks can be used as a conventional filler.Representative examples of such carbon blacks include N110, N121, N134,N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343,N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754,N762, N765, N774, N787, N907, N908, N990 and N991. These carbon blackshave iodine absorptions ranging from 9 to 145 g/kg and DBP numberranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), particulate polymer gels including but notlimited to those disclosed in U.S. Pat. No. 6,242,534; 6,207,757;6,133,364; 6,372,857; 5,395,891; or 6,127,488, and plasticized starchcomposite filler including but not limited to that disclosed in U.S.Pat. No. 5,672,639.

In one embodiment the rubber composition may contain a conventionalsulfur containing organosilicon compound. Examples of suitable sulfurcontaining organosilicon compounds are of the formula:

Z-Alk-S-Alk-Z

in which Z is selected from the group consisting of

where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

In one embodiment, the sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In oneembodiment, the sulfur containing organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and/or3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to formula I,Z may be

where R² is an alkoxy of 2 to 4 carbon atoms, alternatively 2 carbonatoms; alk is a divalent hydrocarbon of 2 to 4 carbon atoms,alternatively with 3 carbon atoms; and n is an integer of from 2 to 5,alternatively 2 or 4.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from GE Silicones.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

The invention is further illustrated by the following nonlimitingexample.

EXAMPLE 1

In this example, the effect of adding a solvent-extracted asphaltene toa rubber composition is illustrated. Rubber compositions containingdiene based elastomer, fillers, process aids, antidegradants, andcuratives were prepared following recipes as shown in Table 1. Sample 1was a control. Sample 2 was identical in composition to sample 1 exceptfor the substitution of 4 phr of asphaltene-containing resin for part ofthe process oil. Sample 3 was identical in composition to sample 1except for the substitution of 4 phr of solvent-extracted asphaltene forpart of the process oil. The samples were tested for cure propertiesusing an MDR 2000 following ASTM D2084 and D5289

Results are given in Table 2. Graphs of torque versus cure time areshown in FIG. 1.

The samples were tested for viscoelastic properties using RPA followingASTM D5289. “RPA” refers to a Rubber Process Analyzer as RPA 2000™instrument by Alpha Technologies, formerly the Flexsys Company andformerly the Monsanto Company. References to an RPA 2000 instrument maybe found in the following publications: H. A. Palowski, et al, RubberWorld, June 1992 and January 1997, as well as Rubber & Plastics News,April 26 and May 10, 1993.

The “RPA” test results in Table 2 are reported as being from dataobtained at 100° C. in a dynamic shear mode at a frequency of 1 hertzand at the reported dynamic strain values. Graphs of shear modulus G′versus strain are shown in FIG. 2. Tensile and hardness properties werealso measured and reported in Table 2.

TABLE 1 Sample No. control comparative invention 1 2 3 Natural Rubber 7070 70 Styrene-Butadiene Rubber 30 30 30 Extender Oil 11.25 11.25 11.25Carbon Black 52.5 52.5 52.5 Reinforcing Resins 4 4 4 Sulfur 2.8 2.8 2.8Accelerator 1.7 1.7 1.7 Zinc Oxide 3 3 3 Stearic Acid 1 1 1 Process Oil5.4 1.4 1.4 Asphaltene-Containing Resin¹ 0 4 0 Solvent-ExtractedAsphaltene² 0 0 4 ¹Struktol 40-MS, reportedly 3 to 5 percent by weightasphaltene ²Extract from Struktol 40-MS, extracted with propane andcrystallized, then purified with n-pentane.

TABLE 2 Sample No. control comparative invention 1 2 3Asphaltene-containing resin, phr 0 4 0 Solvent-extracted asphaltene, phr0 0 4 MDR, 150° C. Max Torque, dN-m 14.7 15.0 15.6 Delta Torque, dN-m13.3 13.5 14.0 Scorch time, min 4.6 5.9 5.4 T25, min 5.6 6.9 6.5 T90,min 9.7 11.5 11.2 RPA, 100° C., 1 Hz G′, 1% strain (MPa) 1.03 1.06 1.11G′, 10% strain (MPa) 0.88 0.90 0.95 G′, 50% strain (MPa) 0.67 0.69 0.72tan delta, 10% strain 0.074 0.081 0.081 Shore A Hardness 23° C. 56 58 59Ring Modulus, 23° C. Elongation at break, % 437 470 400 Modulus 100%,MPa 2.0 1.9 2.1 Modulus 300%, MPa 9.7 8.0 9.0 Tensile Strength, MPa 14.113.1 11.5

As best seen in FIG. 1 and in the data of Table 2, sample 3 containingthe solvent-extracted asphaltene exhibits a different cure behaviorreflected by a higher cure amount (Delta torque). The higherconcentration in sulfur of the solvent-extracted asphaltene affectspositively the cure amount and cure plateau stability. As best seen inFIG. 2, the shear modulus G′ versus strain graph follows a differenttrend for sample 3 containing the solvent-extracted asphaltene. Due toanother kind of reticulation to the polymer network, thesolvent-extracted asphaltene apparently enhances the dynamic stiffnessas expressed by the dynamic shear modulus

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

1. A pneumatic tire comprising at least one component, the at leastcomponent comprising a rubber composition, the rubber compositioncomprising 100 parts by weight of a diene based elastomer and from 1 to20 parts by weight, per 100 parts by weight of elastomer (phr), of asolvent-extracted asphaltene.
 2. The pneumatic tire of claim 1, whereinthe solvent-extracted asphaltene is present in the rubber composition ina concentration ranging from about 1 to about 15 parts by weight, per100 part by weight of elastomer (phr).
 3. The pneumatic tire of claim 1,wherein the solvent-extracted asphaltene comprises greater than 5percent by weight of sulfur, based on the total weight of theasphaltene.
 4. The pneumatic tire of claim 1, wherein thesolvent-extracted asphaltene comprises greater than 7 percent by weightof sulfur, based on the total weight of the asphaltene.
 5. The pneumatictire of claim 1, wherein the solvent-extracted asphaltene comprisesgreater than 8 percent by weight of sulfur, based on the total weight ofthe asphaltene.
 6. The pneumatic tire of claim 1, wherein the dienebased elastomer is selected from the group consisting of cis1,4-polyisoprene rubber (natural or synthetic), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion or solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers. 7.The pneumatic tire of claim 1, wherein the rubber composition furthercomprises from about 10 to about 100 phr of carbon black.
 8. Thepneumatic tire of claim 1, wherein the rubber composition furthercomprises from about 5 to 70 phr of at least one oil selected from thegroup consisting of aromatic, paraffinic, naphthenic, vegetable oils,MES, TDAE, SRAE and heavy naphthenic oils.